1. Field of the Invention
The present disclosure is related to a device packaging method and device package structure, more particularly, to a method of using laser local heating for packaging a sensing element in vacuum to reduce out-gassing during the packaging process.
2. Description of the Related Art
At present, infrared camera have been applied in recording and storing continuous thermal images. The infrared camera comprises a thermal sensing IC which includes a sensing element array. The resistance of each of thermal sensing elements of the sensing element array is changed correspondingly upon receipt of the infrared radiation energy, and it means that resistance change of the thermal sensing element can correspond to strength of thermal energy, so that the thermal sensing element array can generate a thermal image correspondingly to the infrared radiation energy.
To prevent the thermal sensing element array from being affected by heat convection generated in the packaged space, the thermal sensing IC is placed on a base and packaged by a cover and the base, and particularly the packaged space is maintained in vacuum. The sensitivity of the thermal sensing element array is related to vacuum degree of the packaged space.
Please refer to FIG. 1 which illustrates a schematic view of a packaging method in the prior art. In FIG. 1, a sensing element 30 is placed on the bottom of a cavity base 10, and a sealant 90 is disposed between a cover 20 and an edge part of the cavity base 10. In the prior art, the cavity base 10 is heated from the bottom during packaging, and heat is then conducted to the edge part of the cavity base 10 for heating and melting the sealant, so that the cavity base 10 and the cover 20 are bonded to complete packaging.
However, there are some drawbacks in packaging method in the prior art. First, it is easy to damage the sensing element 30 while the bottom of the cavity base 10 is heated continuously, and may cause drop of yield rate. Second, gas is generated easily during heating under the cavity base 10, so the time for exhausting gas must be extended in order to maintain vacuum degree in the packaged space, however, which resulting in undesired longer packaging time. Thirdly, mass out-gassing may occur during heating on whole cavity base 10, which resulting in an undesired longer time for vacuumization. Moreover, longer heating time may cause the sensing element 30 being damaged more easily.
Besides, if the packaging process includes sealing of multiple elements or multiple positions, sealants or solders having different melting points must be used because of integral heating used in the packaging method in the prior art. For consideration to such packaging process using integral heating, the solder having high melting point must be used previous to the solder having low melting point. Such consideration limits the selection for sealant or solder, which resulting in increase of packaging cost.
Moreover, for kind of sensing element such as infrared thermography imager, the sensing sensitivity is in proportion to vacuum degree of packaging. Please refer to FIG. 11 which is a relationship diagram of noise equivalent temperature difference (NETD) and packaging vacuum degree of an infrared thermography imager. In FIG. 11, lower packaging vacuum degree that means higher atmospheric pressure in vacuum, causes higher noise equivalent temperature difference, it indicates that the sensitivity of the infrared thermography imager becomes lower. However, in the prior art, in order to obtain higher packaging vacuum degree, the time required for exhausting gas must be longer, so the packaging time must be extended.